1. Field of the Invention
The present invention relates to a disc driving apparatus for rotationally driving a disc type record medium in an optical disc player or the like, and more particularly relates to the disc driving apparatus having a clamping mechanism for favorably clamping the disc type record medium in a stable manner.
2. Description of the Related Art
When an optical disc is loaded on an optical disc player, the optical disc is clamped and is rotationally driven by the optical disc driving apparatus equipped in the optical disc player.
The optical disc driving apparatus is constructed such that, in order to clamp the optical disc, a loading surface of a turn table abuts to one surface of the loaded optical disc while a circumferential abutting portion of the clamper abuts to the other surface of the loaded optical disc.
More concretely, the circumferential abutting portion of the clamper abuts to a circumferential abutting area 110xe2x80x3 on the surface of an optical disc 1 as shown in FIG. 6. The circumferential abutting area 110xe2x80x3 is located at an inner circumferential area of the surface of the optical disc 1, which is close to a center hole c of the optical disc 1 and at which record information is not recorded. A pressure is applied by the circumferential abutting portion of the clamper to the circumferential abutting area 110xe2x80x3 of the optical disc 1 on the loading surface of the turn table, so as to tightly hold the optical disc 1 while a spindle motor of the optical disc driving apparatus rotationally drives the clamped optical disc 1 by rotating the turn table as well as the clamper.
In the above explained construction, when the optical disc 1 is rotationally driven by the spindle motor, since the optical disc 1 has an inherent vibration mode, the optical disc 1 itself is excited in accompaniment with the rotation of the spindle motor. Particularly, by the vibration component in the frequency range of about 700 Hz to 800 Hz of the optical disc 1, (i) an actuator which drives an objective lens of an optical head for reading the record information on the optical disc 1 in a focus direction and in a tracking direction and (ii) the optical disc 1 resonate. Thus, the vibration due to the resonance is applied to the servo control of the actuator for the focusing control, the tracking control and the like, as an external disturbance, so that the harmful influence is given e.g., the servo cannot be closed.
Here, the vibration mode of the optical disc 1 due to the vibration component in the frequency range of about 700 Hz to 800 Hz at the time of rotationally driving the optical disc 1 is explained with reference to FIGS. 6 and 7. In FIG. 6, a line d-dxe2x80x2 is a line passing through the center c of the optical disc 1, points e and f are on the line d-dxe2x80x2 at the outer circumference of the optical disc 1, a point g is on the line d-dxe2x80x2 between the center c and the point e, a point h is on the line d-dxe2x80x2 between the center c and the point f, and points i and j are on the line d-dxe2x80x2 and in the circumferential abutting area 110xe2x80x3. FIG. 7 is a diagram for explaining a vibration mode of the optical disc 1. More concretely, FIG. 7 schematically shows a section at the line d-dxe2x80x2 of the optical disc 1, in which the form of the optical disc 1 is changed by the vibration as indicated by a solid line C1, a dashed line C2 and a chain line C3.
In FIG. 7, when the optical disc 1 is rotationally driven by the spindle motor, the vibration due to the rotation is transmitted from the turn table and the clamper. At this time, since the optical disc 1 is circumferentially held by the turn table and the clamper at the circumferential abutting area 110xe2x80x3, the vibration transmitted from the spindle motor is radially transmitted over the whole surface of the optical disc 1 from the circumferential abutting area 110xe2x80x3. Therefore, by this transmission of the vibration, at a certain time point, the forces are applied to the point i in a +Y direction and to the point j in a xe2x88x92Y direction, so that the forces are transmitted toward the outer circumference of the optical disc 1 along the line d-dxe2x80x2. This results in that the forces are applied to the points g and h in the +Y and xe2x88x92Y directions respectively. At this time, since the forces in the +Y and xe2x88x92Y directions are not transmitted yet to the points e and f respectively, the optical disc 1 is transiently distorted to have the form indicated by the dashed line C2. On the other hand, at another certain time point, the forces are applied to the points e, f, g and h respectively in the directions reverse to the directions in the above mentioned case, so that the optical disc 1 is transiently distorted to have the form indicated by the chain line C3. Namely, since the forces are applied to the points i and j on the line d-dxe2x80x2 passing through the center c in the directions reverse to each other, the transient distortions indicated by the dashed line C2 and the chain line C3 are alternatively repeated, so that the vibration of the optical disc 1 is generated.
It is therefore an object of the present invention to provide a disc driving apparatus for rotationally driving a disc type record medium, which can restrain the resonance due to a vibration mode of the disc type record medium, e.g., the resonance in a frequency range of about 700 Hz to 800 Hz when rotationally driving the disc type record medium.
The above object of the present invention can be achieved by a disc driving apparatus provided with: a turn table on which a disc type record medium is loaded; a clamper opposed to the turn table for clamping the disc type record medium on the turn table by means of a magnetic force applied between the turn table and the clamper; and a spindle motor for rotationally driving the turn table, the clamper comprising at least 3 abutting portions for abutting to the disc type record medium such that only one of the abutting portions is respectively on a line passing through a center of the clamper in a plain parallel to a record surface of the disc type record medium.
According to the disc driving apparatus of the present invention, the disc type record medium is loaded on the turn table, and is clamped by the clamper on the turn table by means of the magnetic force applied therebetween. Then, the turn table is rotationally driven by the spindle motor. At this time, the clamper has at least 3 abutting portions such that only one of the abutting portions is respectively on the line passing through the center of the clamper. Namely, any two of the abutting portions are not on a same line passing through the center of the clamper but are on different lines passing through the center of the clamper. Thus, on each of the lines passing though the center of the disc type record medium, the forces are not simultaneously applied in the directions different from each other. Accordingly, the vibration of the inherent vibration mode of the disc type record medium, e.g., the vibration in a frequency range of about 700 Hz to 800 Hz, when rotationally driving the disc type record medium, can be certainly restrained.
In one aspect of the disc driving apparatus of the present invention, the turn table has a circumferential loading surface for loading the disc type record medium thereon, and each of the abutting portions is shaped in a sector disposed substantially at equiangular positions in a circumference direction of the clamper.
According to this aspect, the disc type record medium can be clamped in a stable manner while the vibration of the inherent vibration mode of the disc type record medium can be certainly restrained.
In another aspect of the disc driving apparatus of the present invention, the turn table is provided with: a hub having a cylindrical engaging portion for engaging with a center hole of the disc type record medium and a taper portion for guiding the center hole to the cylindrical engaging portion; and a circumferential loading surface for loading the disc type record medium thereon, and the clamper is provided with: a taper portion proximate to the taper portion of the hub when clamping the disc type record medium; and a proximity portion, which is formed at a connection between the taper portion of the clamper and each of the abutting portions and is disposed more proximate to the hub than the taper portion of the clamper in a radial direction of the disc type record medium.
According to this aspect, by virtue of the proximity portion, it is possible to restrain the backlash of the disc type record medium and the clamper due to the reduction in an abutting area in the circumferential direction of the disc type record medium.
In another aspect of the disc driving apparatus of the present invention, the clamper has a yoke for receiving the magnetic force from the hub and absorbing the clamper onto the turn table.
According to this aspect, the disc type record medium can be clamped in a stable manner by means of the magnetic force between the clamper and the turn table. In this case, the magneto may be built in the turn table. Alternatively, the turn table may have a yoke while the magneto may be built in the clamper.
In another aspect of the disc driving apparatus of the present invention, each of the abutting portions has such a shape that two sectors, each of which has a center thereof at the center of the clamper, are combined together in a radial direction of the clamper.
According to this aspect, by virtue of the abutting portions each having the specific shape, the disc type record medium can be clamped in a stable manner.